A pressurized-water reactor (PWR) used in a nuclear power plant is composed of a pressure vessel for containing nuclear fuel, a pressurizer, a steam generator for generating secondary steam, and a reactor coolant pump (RCP), etc. Through driving of the reactor coolant pump, coolant (fluid) flows in a cyclic path that connects the pressure vessel, the pressurizer, and the steam generator. Then, secondary steam generated at the steam generator drives a turbine, thereby generating electricity.
As a shaft sealing structure for a main shaft in the reactor coolant pump, three seals are provided in the axial direction on the circumference of the shaft, for example. As the seals, a first seal (No. 1 Seal), a second seal (No. 2 Seal), and a third seal (No. 3 Seal) are arranged in this order from an inner side of the pump toward an outer side thereof. Thus, in the reactor coolant pump, while the main shaft is rotated in a seal housing, sealing is achieved between the inside of a pump housing and the outside of the seal housing.